Method for preparing acryl based impact-reinforcement

ABSTRACT

The present invention relates to a preparation method of an acryl-based impact-reinforcement, and more particularly, to a preparation method of an acryl-based reinforcement prepared by blending latex having large particles and latex having small particles, being capable of enhancing impact-resistance of a polyvinyl chloride (PVC) resin. The present invention provides a method of preparing an acryl-based impact reinforcement comprising a step of blending a) 50 to 90 parts by weight of latex having large particles with a particle size of 200 to 500 nm and a core-shell structure and b) 10 to 50 parts by weight of latex having small particles with a particle size of 60 to 140 nm and a core-shell structure. In addition, the present invention provides an impact-reinforcement prepared by the method of the present invention, and a polyvinyl chloride (PVC) composition comprising the same.

CROSS REFERENCE TO RELATED APPLICATION

This application is based on application No. 2000-76010 filed in theKorean Industrial Property Office on Dec. 13, 2000, the content of whichis incorporated hereinto by reference.

BACKGROUND OF THE INVENTION

(a) Field of the Invention

The present invention relates to a preparation method of an acryl-basedimpact-reinforcement, and more particularly, to a preparation method ofan acryl-based impact-reinforcement, in which latex having largeparticles and latex having small particles are blended together toenable the enhancement of an impact-resistance of a polyvinylchloride(PVC) resin.

(b) Description of the Related Art

An impact-reinforcement is used for enhancing the impact-resistance ofthe polyvinyl chloride resins, and the different types ofimpact-reinforcement include a methylmethacrylate-butadiene-styrene-based (MBS) resin, a chlorinatedpolyethylene-based (CPE) resin, and an acryl-based resin. Among theseresins, the acryl-based resin is widely used for products exposed to thesun, since it has a high weather-resistance. For example, PVC windowsash needs both high impact-resistance and weather-resistance, andimpact reinforcement which is prepared by grafting a rubbery elastomercore comprising alkyl acrylate polymer with a glassy methacryl-basedpolymer shell that is highly compatible to the PVC resin showed bothnecessary properties.

The manner in which the core is bonded with the shell chemically is acritical factor in realizing beneficial properties of acryl-based impactreinforcements with the core-shell structure. In addition, the degree ofcross-linking of dispersed rubber particles in matrix, the content ofrubber particles, the size of rubber particles, and the swelling indexof rubber particles to solvent are critical factors that affect theimpact resistance of acryl-based impact reinforcements.

In order to enhance the impact resistance of polyvinyl chloride resin,an acryl-based impact reinforcement has been prepared by emulsionpolymerization which includes both core and shell polymerization.

In the core polymerization, alkyl acrylate monomers having one doublebond and low glass transition temperature are polymerized, and the alkylacrylate polymer gives an acryl-based impact reinforcement with bothweather-resistance due to the absence double bond after polymerizationand impact-resistance due to the low glass transition temperature.Cross-linking agents give impact resistance to the impact reinforcementdue to the formation of the rubber structure on the impactreinforcement. The cross-linking agent also provides a latex stabilityduring the polymerization reaction, and it enables the core to maintaina spherical form during the processing steps.

The shell polymerization is generally performed by graft-polymerizingalkyl methacrylate monomer, which is highly compatible with polyvinylchloride resin, on the core. To increase a dispersibility of theimpact-reinforcement, the shell may contain small amount of anacrylonitrile monomer.

Two preparation methods of the acryl-based impact reinforcement, whichis prepared by emulsion polymerization, are disclosed. U.S. Pat. No.5,612,413 discloses a method, in which the impact reinforcement isprepared by multi-step-emulsion polymerization that includespolymerization of a seed having small particles, polymerization ofmonomers in two or four steps to grow the seed, and polymerization ofmonomers used for a shell therein in order to form a core-shellstructure wherein the core is enclosed within the shell. European PatentNo. 0,522,605A discloses a method, in which an impact reinforcement isprepared by a micro-agglomeration method comprising polymerizing a latexhaving a core-shell structure with a particle size of 100 nm or less,agglomerating the particles to prepare a latex with a desired particlesize, and forming a capsulated shell on the agglomerated particles.

However, there is a need to develop an impact reinforcement which havean enhanced impact resistance to be used in place of the impactreinforcement prepared by the conventional method.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an acryl-basedimpact-reinforcement capable of enhancing an impact resistance.

It is another object to provide a preparation method of an acryl-basedimpact-reinforcement for a polyvinyl chloride resin capable ofmaximizing an impact strength by controlling the content and size ofrubber particles, the distance between the rubber particles, and theswelling index of the rubber particles.

In order to achieve these objects, the present invention provides apreparation method of an acryl-based impact-reinforcement comprisingblending a) 50 to 90 parts by weight of latex having large particleswith a particle size of 200 to 500 nm and a core-shell structure; and b)10 to 50 parts by weight of latex having small particles with a particlesize of 60 to 140 nm and a core-shell structure.

In addition, the present invention further provides a polyvinyl chlorideresin compound prepared by using the invented impact reinforcement.

DETAILED DESCRIPTION OF THE INVENTION

In the following detailed description, only the preferred embodiment ofthe invention has been shown and described, simply by way ofillustration of the best mode contemplated by the inventors of carryingout the invention. As will be realized, the invention is capable ofmodification in various obvious respects, all without departing from theinvention. Accordingly, the drawings and description are to be regardedas illustrative in nature, and not restrictive.

An acryl-based impact-reinforcement of the present invention is preparedby controlling the rubber particle content, the rubber particle size,the distance between rubber particles, and the swelling index of therubber particles, all of which are critical factors in determiningimpact strength of polyvinyl chloride resin. In addition, theacryl-based impact-reinforcement is prepared by polymerizing latexhaving large particles and latex having small particles respectively,and blending the two latexes.

The effect of the rubber particle size on impact resistance will bedescribed. To prepare an impact reinforcement having impact resistancein a matrix, it is necessary that a distance between particles ismaintained below a characteristic distance and that particle size ismaximized. Therefore, when the particle size of an impact reinforcementis small (below 100 nm), the impact resistance of the impactreinforcement decreases because the particle size is small, although theinter-particle distance is below the characteristic distance, and whenthe particle size of an impact reinforcement is large (greater than 300nm), the impact resistance of the impact reinforcement decreases becausethe distance between particles is above the characteristic distance.

Therefore, the acryl-based impact reinforcement of the present inventionis prepared by blending a latex having large particles to enhance impactresistance with a latex having small particles to decrease the distancebetween particles below the characteristic distance.

The swelling index is a coefficient of swelling degree of a solvent ingel, and an index of free volume of a polymer. As the cross-linkingdensity of rubber is increased, the swelling index decreases, and as thecross-linking density of rubber is decreased, the swelling indexincreases. The cross-linking density may be controlled by amount of thecross-linking agent used in preparing rubber, and as the amount of thecross-linking agent is decreased to increase the swelling index, agreater impact resistance is realized. However, when the amount of thecross-linking agent is too small, it is difficult to control theswelling index since the latex stability decreases during thepolymerization reaction. In the present invention, latex having largeand small particles with a swelling index of 2.0 to 12.0 is preferablyused.

The acryl-based impact reinforcement is prepared by polymerizing a seed,adding monomers used for the core thereto twice to four times to growthe core rubber particle, adding monomers used for the shell theretoenclosing the core within the shell. In order to prepare a latex havinglarge particles with a particle size of 200 to 500 nm and a latex havingsmall particles with a particle size of 60 to 140 nm, the samepreparation method but the amount of emulsifying agent was used andmixed the latexes having large particles and small particles in a weightratio of 5 to 9:1 to 5, and coagulated.

It is preferable that a) latex having large particles and b) latexhaving small particles respectively comprises a core having i) 97.0 to99.9 parts by weight of alkyl acrylate with its alkyl group of C₂ to C₈;and ii) 0.1 to 3.0 parts by weight of cross-linking agent.

i) The alkyl acrylate preferably includes a monomer selected from thegroup consisting of methyl acrylate, ethyl acrylate, propyl acrylate,isopropyl acrylate, butyl acrylate, hexyl acrylate, octyl acrylate, and2-ethylhexyl acrylate; and a homopolymer or a copolymer thereof, andmore preferably the alkyl acrylate includes butyl acrylate, 2-ethylhexylacrylate, or a mixture thereof.

ii) The cross-linking agent preferably includes at least one monomerselected from the group consisting of 1,3-butanediol diacrylate,1,3-butanediol dimethacrylate, 1,4-butandiol diacrylate, 1,4-butanedioldimethacrylate, allyl acrylate, allyl methacrylate, trimethylol propanetriacrylate, tetraethylene glycol diacrylate, tetraethylene glycoldimethacrylate, and divinyl benzene; and a homopolymer or a copolymerthereof. More preferably, the cross-linking agent includes1,3-butanediol diacrylate, 1,3-butanediol dimethacrylate, allylacrylate, allyl methacrylate, or a mixture thereof. The content of thecross-linking agent ranges from 0.1 to 5.0 parts by weight based on theweight of the monomer of the present invention. When the content of thecross-linking agent is below 0.1 parts by weight based on the parts byweight of the whole polymer, the spherical particles are easy to deformduring processing, and when the content of the cross-linking agent isover 5.0 parts by weight based on the parts by weight of the wholepolymer, the core of the impact-reinforcement exhibits brittlecharacteristics such that the impact-reinforcing capabilitydeteriorates.

a) The latex having large particles and b) the latex having smallparticles respectively comprised of a shell having i) 80 to 100 parts byweight of the alkyl methacrylate with a carbon number of 1 to 4, theyfurther comprised of ii) ethyl acrylate, methyl acrylate, and butylacrylate (a content of which is below 10 parts by weight) in order tocontrol a glass transition temperature of the shell, and they may becomprised of iii) nitrites such as acrylonitrile and methacrylonitrile(a content of which is below 10 parts by weight) in order to enhance amiscibility of the shell with matrix.

In addition, the latex having large particles and the latex having smallparticles comprise rubber monomer having 70 to 95 wt % of its contentbased on that of the total monomer. When the rubber content of theimpact reinforcement is below 70 wt %, the impact-reinforcementcharacteristics may deteriorate since the impact-reinforcement has asmall amount of rubber, and when the content of the monomer rubber isover 95 wt %, the impact resistance characteristics may deterioratesince the amount of the shell is insufficient to encapsulate the core,and it is difficult for the rubber to well dispersed in matrix.

The acryl-based impact-reinforcement of the present invention isprepared by blending the latex having large particles and the latexhaving small particles. During blending, the latex having largeparticles is added to the latex having small particles. The blendedlatex is coagulated with an electrolyte preferably such as calciumchloride, after which filtering is performed to obtain theimpact-reinforcement.

A compound composition for polyvinyl chloride resin having goodimpact-reinforcement comprises a) 80 to 99 parts by weight of polyvinylchloride resin; and b) 1 to 20 parts by weight of the acryl-basedimpact-reinforcement.

Hereinafter, the preparation method of the acryl-basedimpact-reinforcement will be described in detail. The preparation methodcomprises main steps as follows:

1) Preparation of Latex Having Large Particles

The preparation method of the latex having large particles comprises,

i) first polymerization of seed by cross-linking a mixture comprising97.0 to 99.9 parts by weight of alkyl acrylate with carbon number of 2to 8; 0.1 to 3.0 parts by weight of cross-linking agent; 0.01 to 3.0parts by weight of an initiator; 0.1 to 10.0 parts by weight of anemulsifying agent; and 1000.0 parts by weight of ion-exchange water at atemperature of 60 to 80° C.;

ii) second polymerization of core rubber by emulsifying a mixturecomprising 97.0 to 99.9 parts by weight of alkyl acrylate with carbonnumber of 2 to 8; 0.1 to 3.0 parts by weight of cross-linking agent; 0.1to 4.0 parts by weight of an emulsifying agent; and 80 parts by weightof ion-exchange water, and adding the emulsified mixture to the seedcontinuously while adding 0.01 to 3.0 parts by weight of an initiatorthereto, and polymerizing these elements together;

iii) third polymerization of core rubber by emulsifying a mixturecomprising 97.0 to 99.9 parts by weight of alkyl acrylate with carbonnumber of 2 to 8; 0.1 to 3.0 parts by weight of cross-linking agent; 0.1to 4.0 parts by weight of an emulsifying agent; and 80 parts by weightof ion-exchange water, and adding the emulsified mixture to the secondpolymer continuously while adding 0.01 to 3.0 parts by weight of aninitiator thereto, and polymerizing these elements together; and

iv) fourth polymerization of a shell by emulsifying a mixture comprising80 to 100 parts by weight of alkyl methacrylate with carbon number of 1to 4; 10 parts by weight or less of alkyl acrylate selected from thegroup consisting of ethyl acrylate, methyl acrylate, and butyl acrylate;10 parts by weight or less of nitrile selected from the group consistingof acrylonitrile and methacrylonitrile; 0.1 to 4.0 parts by weight of anemulsifying agent; and 150 parts by weight of ion-exchange water, andadding the emulsified mixture to the core continuously while adding 0.01to 3.0 parts by weight of an initiator thereto, and polymerizing theseelements together in order to form the shell.

2) Preparation of Latex Having Small Particles

The preparation procedure of latex having small particles is the same asthat of latex having large particles. That is, the preparation of latexhaving small particles comprises,

i) first polymerization of seed by cross-linking a mixture comprising97.0 to 99.9 parts by weight of alkyl acrylate with carbon number of 2to 8; 0.1 to 3.0 parts by weight of cross-linking agent; 0.01 to 3.0parts by weight of an initiator; 20 to 80 parts by weight of anemulsifying agent; and 1000.0 parts by weight of ion-exchange water at atemperature of 60 to 80° C.;

ii) second polymerization of core rubber by emulsifying a mixturecomprising 97.0 to 99.9 parts by weight of alkyl acrylate with carbonnumber of 2 to 8; 0.1 to 3.0 parts by weight of cross-linking agent; 0.1to 4.0 parts by weight of an emulsifying agent; and 80 parts by weightof ion-exchange water, and adding the emulsified mixture to the seedcontinuously while adding 0.01 to 3.0 parts by weight of an initiatorthereto, and polymerizing these elements together;

iii) third polymerization of core rubber by emulsifying a mixturecomprising 97.0 to 99.9 parts by weight of alkyl acrylate with carbonnumber of 2 to 8; 0.1 to 3.0 parts by weight of cross-linking agent; 0.1to 4.0 parts by weight of an emulsifying agent; and 80 parts by weightof ion-exchange water, and adding the emulsified mixture to the secondpolymer continuously while adding 0.01 to 3.0 parts by weight of aninitiator thereto, and polymerizing these elements together; and

iv) fourth polymerization of a shell by emulsifying a mixture comprising80 to 100 parts by weight of alkyl methacrylate with carbon number of 1to 4; 10 parts by weight or less of alkyl acrylate selected from thegroup consisting of ethyl acrylate, methyl acrylate, and butyl acrylate;10 parts by weight or less of nitrile selected from the group consistingof acrylonitrile and methacrylonitrile; 0.1 to 4.0 parts by weight of anemulsifying agent; and 150 part by weight of ion-exchange water, andadding the emulsified mixture to the core continuously while adding 0.01to 3.0 parts by weight of an initiator thereto, and polymerizing theseelements together in order to form the shell.

Any chemical that is capable of initiating polymerization reaction canbe used for the initiator in the preparation of the latex having largeparticles or small particles, and exemplary initiators include ammoniumpersulfate, potassium persulfate, azobisbutyronitrile, benzoyl peroxide,butyl hydroperoxide, and cumene hydroperoxide.

Ionic emulsifier or non-ionic emulsifier may be used as an emulsifyingagent applied in the preparation of the latex having large particles orsmall particles: the ionic emulsifier includes unsaturated fatty acidpotassium salt, oleic acid potassium salt, sodium lauryl sulfate (SLS),and sodium dodecyl benzene sulfate (SDBS).

3) Preparation of an Acryl-based Impact-reinforcement

The latex having large particles and the latex having small particlesare blended at a ratio of 5 to 9:1 to 5, and ion-exchange water is addedthereto in order to lower the solid content of the mixture to 10 wt %.10 wt % of a calcium chloride solution is added to the mixture in orderto coagulate the polymer particles. The temperature of the coagulatedslurry is elevated to 90° C. and the slurry is aged and cooled. Thecooled slurry is cleaned with ion-exchange water, and filtered to obtainthe acryl-based impact-reinforcement.

The following Examples illustrate the present invention in furtherdetail. However, it is to understand that the present invention is notlimited by these Examples.

EXAMPLE 1

1) First Polymerization

461.3 g of ion-exchange water was added into a reactor, and thetemperature of the reactor was elevated to 75° C. When the temperatureof the ion-exchange water in reactor reached 75° C., 49.3 g of butylacrylate, 0.25 g of allyl methacrylate, 0.5 g of 1,3-butandioldimethacrylate, and 31.2 g of stearic acid potassium salt (8 wt %solution) were added to the reactor. While maintaining the reactortemperature at 75° C., 0.42 g of potassium persulfate dissolved in 10 gof the ion-exchange water was added in order to initiate thepolymerization reaction and prepare the seed. The particle size of theprepared latex was measured by laser light scattering (NICOMP), and itwas 90 nm.

2) Second Reaction

366.7 g of ion-exchange water, 541.8 g of butyl acrylate, 2.75 g ofallyl methacrylate, and 5.5 g of 1,3-butandiol dimethacrylate, 68.8 g ofsteric acid potassium salt (8 wt % solution) were mixed together inorder to prepare an emulsified mixture. Keeping the emulsified mixturecontinuously added into the seed latex at a constant rate for 3 hours,0.5 g of the potassium persulfate dissolved in 10 g of ion-exchangewater was further added therein at a constant rate for 3 hours toprocede core polymerization reaction.

3) Third Reaction

121.2 g of ion-exchange water, 197.0 g of butyl acrylate, 1.0 g of allylmethacrylate, 2.0 g of 1,3-butandiol dimethacrylate, and 31.3 g ofstearic acid potassium salt (8 wt % solution) were mixed together inorder to emulsify a mixture thereof. The emulsified mixture was added tothe latex prepared by the second reaction continuously for 1 hour at aconstant flow rate. Simultaneously, 0.37 g of potassium persulfatedissolved in 10 g of ion-exchange water was added thereto continuouslyfor 1 hour. The reaction mixture was aged for 1 hour while maintaining areactor temperature at 75° C.

4) Fourth Reaction

To form a shell on the core of the third reaction, 267.0 g ofion-exchange water, 182.6 g of methyl methacrylate, 10.0 g of ethylacrylate, 7.4 g of acrylonitrile, 25.0 g of stearic acid potassium salt(8 wt % solution) were emulsified. The emulsion and 0.5 g of potassiumpersulfate dissolved in 10 g of ion-exchange water were added to themixture of the third reaction continuously for 1.5 hours. The reactionmixture was further aged for 1 hour while maintaining a reactortemperature of 75° C., resulting in a final latex. The particle size ofthe final latex was 250 nm.

EXAMPLE 2

The amount of 1,3-butandiol dimethacrylate added in the first to thirdreactions of Example 1 was decreased by ½ in order to increase theswelling index of the impact reinforcement. Except the aforementioned,the latex was prepared by the same method as in Example 1.

EXAMPLE 3

The 1,3-butandiol dimethacrylate added in the first to third reactionsof Example 1 was not used in order to further increase the swellingindex of the impact reinforcement. Except the aforementioned, the latexwas prepared by the same method as in Example 1.

EXAMPLES 4 to 12

Latex having particle size of 350 nm, 80 nm, and 120 nm wererespectively prepared by controlling the amount of stearic acidpotassium salt added in the first reaction of Example 1. In addition,the amount of 1,3-butandiol dimethacrylate was decreased as the samemanner in Example 2 and 3 in order to change the swelling index of theimpact reinforcement. Except the aforementioned, the latex was preparedby the same method as in Example 1. The amounts of stearic acidpotassium salt and 1,3-butandiol dimethacrylate in the first step tothird step, and the final particle sizes of each latex according toExamples 4 to 12 are shown in Table 1.

TABLE 1 Amount of stearic Amount of 1,3-butandiol acid dimethacrylate(g) potassium 1^(st) 2^(nd) 3^(rd) Particle size Example salt (g)reaction reaction reaction of latex (nm) 4 21.3 0.5 5.5 2.0 350 5 21.30.25 2.75 1.0 350 6 21.3 0 0 0 350 7 375 0.5 5.5 2.0 80 8 375 0.25 2.751.0 80 9 375 0 0 0 80 10 112 0.5 5.5 2.0 120 11 112 0.25 2.75 1.0 120 12112 0 0 0 120

EXAMPLE 13

In order to compare the impact strength of each Example, a standardlatex having particle size of 200 nm was prepared by controlling theamount of stearic acid potassium salt (8 wt % solution) added in thefirst reaction of Example 1 to 66.0 g and the 1,3-butandioldimethacrylate used in the first to third reactions was not added, as inExample 3. Except the aforementioned, the latex was prepared by the samemethod as in Example

EXPERIMENTAL EXAMPLE

Measurement of a Swelling Index of Latex

Polymerization results and swelling indexes of the latex according toExamples 1 to 13 are shown in Table 2. The swelling index of the latexwas measured after coagulating the latex.

Ion-exchange water was added to the latex of Examples 1 to 13 in orderto decrease the solid content of the latex to 10 wt %, and 4 parts byweight of a 10 wt % calcium chloride solution was added once thereto inorder to coagulate the latex. The temperature of each coagulated slurrywas elevated to 90° C. to age for 10 minutes, after which the slurry wascooled. The coagulated particles were cleaned with ion-exchange watertwo or three times in order to remove by-products from the latex, thenit was filtered to obtain the impact reinforcement. The coagulatedimpact reinforcement was dried by using a fluidized bed dryer (FBD) at85° C. for 2 hours to obtain the impact reinforcement powder.

4.0 g of the impact reinforcement powder were swelled in 130.0 g ofacetone for 50 hours to measure the swelling index of the impactreinforcement. The swelled mixture was then centrifuged at 0° C. and1600 rpm for 2 hours to obtain the swelled gel, and the mass of theswelled gel (A) was measured. In addition, after evaporating theacetone, the mass of the pure gel with the acetone removed (B) wasmeasured, and the swelling index (=A/B) was calculated.

Evaluation of Impact Reinforcement Properties

100 parts by weight of polyvinyl chloride resin (PVC, a product by LGChem., LS-100, degree of polymerization=1000), 4.0 parts by weight ofDLP, 0.9 parts by weight of calcium stearate (Ca-St), 1.36 parts byweight of polyethylene wax (PE wax), 1.0 parts by weight of a processingaid (a product by LG Chem., PA-821), 5.0 parts by weight of CaCO₃, and4.0 parts by weight of TiO₂ were added into a mixer at room temperatureand mixed at 1000 rpm while elevating the temperature to 115° C. Whenthe temperature reached 115° C., the mixing rate was slowed down to 400rpm and the mixture was cooled to 40° C. to obtain a master batch.

7 parts by weight of the impact reinforcement of the Examples wererespectively added to the master batch, and the resulting material wasprocessed by using a 2-roll-mill at 190° C. for 7 minutes to shape thematerial into a sheet with a thickness of 0.6 mm. The sheet was cut to asize of 150 mm by 200 mm, and molded in a mold of 3 mm by 170 mm by 220mm. The molded sheet with a thickness of 3 mm was prepared by preheatinga hot press at 195° C. for 8 minutes (0.5 kg), pressing the sheet withthe hot press for 4 minutes (10 kg), cooling the sheet down for 3minutes (10 kg).

The obtained sheet was cut delicately according to the ASTM D-256standard to prepare specimen for the impact test, and its Izod impactstrength was measured. The test results of Examples 1 to 13 arerepresented in Table 2.

TABLE 2 Particle Cross-linking Swelling Izod impact test Examples size(mm) agent (wt %) index (kg · cm/cm) Example 1 250 1.5 3.1 30.3 Example2 250 1.0 5.3 38.5 Example 3 250 0.5 8.7 47.3 Example 4 350 1.5 3.1 35.7Example 5 350 1.0 5.4 38.4 Example 6 350 0.5 8.8 42.5 Example 7 80 1.53.0 24.7 Example 8 80 1.0 5.2 26.9 Example 9 80 0.5 8.6 29.4 Example 10120 1.5 3.0 28.1 Example 11 120 1.0 5.1 30.1 Example 12 120 0.5 8.7 33.7Example 13 200 0.5 8.7 50.9

EXAMPLES 14 to 17

Each of two latexes having large particle with particle size of 250 nmand the swelling index of 8.7 according to Example 3 and with particlesize of 350 nm and the swelling index of 8.8 according to Example 6 wasblended a weight ratio of 10:0, 7:3, 5:5, 3:7, and 0:10 with each of twolatexes having small particle with particle size of 80 nm and theswelling index of 8.6 according to Example 9 and with particle size of120 nm and the swelling index of 8.7 according to Example 12. Eachblended latex was coagulated to prepare impact reinforcement powder andspecimen was prepared with the same method of Evaluation of impactreinforcement properties. The test results of each blended impactreinforcement are shown in Table 3.

TABLE 3 Latex having Impact strength (kg · cm/cm) with large particles +Latex mixing ratio of latex having large having particles:latex havingsmall particles small particles 10:0 9:1 8:2 7:3 6:4 5:5 3:7 0:10Example Example 3 + 47.3 54.3 55.1 53.7 51.5 48.7 38.2 29.4 14 Example 9Example Example 3 + 47.3 53.0 54.3 55.4 53.5 50.1 42.0 33.7 15 Example12 Example Example 6 + 42.5 50.9 55.8 54.3 52.5 50.6 42.9 29.4 16Example 9 Example Example 6 + 42.5 49.2 52.5 55.6 55.5 51.7 40.3 33.7 17Example 12

As shown in Table 3, when the blending ratio of latexes having largeparticles and small particles was in the range of 5 to 9:1 to 5, theimpact strength was high, and the impact reinforcement of the presentinvention showed enhanced impact-resistance compared to the standardimpact reinforcement of particle size of 200 nm according to Example 13(cf. 10 Table 2).

EXAMPLES 18 to 21

Each of two latexes having large particle with particle size of 350 nmand the swelling index of 3.1 according to Example 4 and with particlesize of 350 nm and the swelling index of 8.8 according to Example 6 wasblended at a weight ratio of 10:0, 7:3, 5:5, 3:7, and 0:10 with each oftwo latexes having small particles with particle size of 80 nm and theswelling index of 3.0 according to Example 7 and with particle size of80 nm and the swelling index of 8.6 according to Example 9, to prepareimpact reinforcement having different particle sizes and swellingindexes. The impact strength of the each impact reinforcement wasmeasured and represented in Table 4.

TABLE 4 Impact strength (kg · cm/cm) Latex having large with mixingratio of latex particles + Latex having large particles:latex havingsmall having small particles particles 10:0 7:3 5:5 3:7 0:10 ExampleExample 4 + 35.7 43.3 40.1 34.8 24.7 18 Example 7 Example Example 4 +35.7 48.2 43.4 36.9 29.4 19 Example 9 Example Example 6 + 42.5 53.6 48.538.4 24.7 20 Example 7 Example Example 6 + 42.5 54.3 50.6 41.3 29.4 21Example 9

As shown in Table 4, the latex having large particles with differentswelling index is mixed with the latex having small particles withdifferent swelling index to prepare an impact reinforcement, in whichthe impact resistance of the impact reinforcement increases when thelarge particle mass ratio is in the range of 50 to 90% in the case whereits large particle size ranges from 250 to 400 nm and its small particlesize ranges from 80 to 120 nm. In addition, comparing the impactresistance of Example 18 to that of Example 19, the impact strength ishigher in Example 18 where the swelling index of the latex ranges from 8to 9.

A preparation method of the present invention relates to a method ofpreparing an acryl-based impact reinforcement having an enhanced impactstrength resulting from controlling the rubber content, the size of therubber particles, the distance between the rubber particles, and theswelling index of the rubber particles.

While the present invention has been described in detail with referenceto the preferred embodiments, those skilled in the art will appreciatethat various modifications and substitutions can be made thereto withoutdeparting from the spirit and scope of the present invention as setforth in the appended claims.

1. A method of preparing an acryl-based impact reinforcement comprising the step of blending: a) 50 to 90 parts by weight of latex having large particles with a mean particle size of 200 to 500 nm and a core-shell structure; and b) 10 to 50 parts by weight of latex having small particles with a mean particle size of 60 to 140 nm and a core-shell structure; wherein the core-shell structure of the large particles is formed by a polymerization method comprising: i) polymerization of a first emulsified mixture comprising 97.0 to 99.9 parts by weight of alkyl acrylate having an alkyl group of C₂ to C₈; 0.1 to 3.0 parts by weight of cross-linking agent; 0.01 to 3.0 parts by weight of a polymerization initiator; 0.1 to 10.0 parts by weight of an emulsifier; and 1000.0 parts by weight of ion-exchange water at 60 to 80° C. to prepare a first seed comprising a first latex; ii) polymerization of a second emulsified mixture comprising 97.0 to 99.9 parts by weight of alkyl acrylate having an alkyl group of C₂ to C₈; 0.1 to 3.0 parts by weight of cross-linking agent; 0.1 to 4.0 parts by weight of an emulsifier; and 80 parts by weight of ion-exchange water, by adding 0.01 to 3.0 parts by weight of a polymerization initiator to the first seed while adding the second emulsified mixture continuously to the seed, to form a second latex; iii) polymerization of a third emulsified mixture comprising 97.0 to 99.9 parts by weight of alkyl acrylate having an alkyl group of C₂ to C₈; 0.1 to 3.0 parts by weight of cross-linking agent; 0.1 to 4.0 parts by weight of an emulsifier; and 80 parts by weight of ion-exchange water, by adding 0.01 to 3.0 parts by weight of a polymerization initiator to the second latex while adding the third emulsified mixture continuously to the second latex, to form a third latex; and iv) polymerization of a fourth emulsified mixture comprising 80 to 100 parts by weight of alkyl methacrylate having an alkyl group of C₁ to C₄; 10 parts by weight or less of alkyl acrylate selected from the group consisting of ethyl acrylate, methyl acrylate, and butyl acrylate; 10 parts by weight or less of nitrile selected from the group consisting of acrylonitrile, and methacrylonitrile; 0.1 to 4.0 parts by weight of emulsifier; and 150 parts by weight of ion-exchange water, by adding 0.01 to 3.0 parts by weight of a polymerization initiator to the third latex while adding the fourth emulsified mixture continuously to the third latex.
 2. The method of preparing an acryl-based impact reinforcement according to claim 1 wherein the swelling index of a) latex having large particles and b) latex having small particles respectively ranges from 2.0 to 12.0.
 3. The method of preparing an acryl-based impact reinforcement according to claim 1 wherein the rubber content of the cores of a) latex having large particles and b) latex having small particles respectively ranges from 70 to 95 wt % based on a total content of the acryl-based impact reinforcement.
 4. The method of preparing an acryl-based impact reinforcement according to claim 1 wherein the cores of latex having large and small particles respectively comprises i) 97.0 to 99.9 parts by weight of alkyl acrylate having an alkyl group of C₂ to C₈; and ii) 0.1 to 3.0 parts by weight of cross-linking agent.
 5. The method of preparing an acryl-based impact reinforcement according to claim 4 wherein the alkyl acrylate is one or more monomers selected from the group consisting of methyl acrylate, ethyl acrylate, propyl acrylate, isopropyl acrylate, butyl acrylate, hexyl acrylate, octyl acrylate, and 2-ethylhexyl acrylate, and a homopolymer thereof or a copolymer thereof.
 6. The method of preparing an acryl-based impact reinforcement according to claim 4 wherein the cross-linking agent is one or more monomers selected from the group consisting of 1,3-butandiol diacrylate, 1,3-butandiol dimethacrylate, 1,4-butandiol diacrylate, 1,4-butandiol dimethacrylate, allyl acrylate, allyl methacrylate, trimethylol propane triacrylate, tetraethylene glycol diacrylate, tetraethylene glycol dimethacrylate, and divinylbenzene, and a homopolymer thereof or a copolymer thereof.
 7. The method of preparing an acryl-based impact reinforcement according to claim 1 wherein each shell of latex having large particles and latex having small particles comprises: i) 80 to 100 parts by weight of alkyl methacrylate having an alkyl group of C₁ to C₄; ii) 10 parts by weight or less of alkyl acrylate selected from the group consisting of ethyl acrylate, methyl acrylate, and butyl acrylate; and iii) 10 parts by weight or less of nitrile selected from the group consisting of acrylonitrile and methacrylonitrile.
 8. The method of preparing an acryl-based impact reinforcement according to claim 1 wherein the blending step is performed by adding latex having large particles to latex having small particles, coagulating a resulting mixture with an electrolyte, and filtering the coagulated slurry to obtain an impact reinforcement.
 9. The method of preparing an acryl-based impact reinforcement according to claim 8 wherein the electrolyte is calcium chloride.
 10. The method of preparing an acryl-based impact reinforcement according to claim 1 wherein the emulsifier is selected from the group consisting of unsaturated fatty acid potassium salt, oleic acid potassium salt, an ionic emulsifier, and a nonionic emulsifier.
 11. The method of preparing an acryl-based impact reinforcement according to claim 1 wherein the polymerization initiator is selected from the group consisting of ammonium persulfate, potassium persulfate, benzoyl peroxide, azobis butyronitrile, butyl hydroperoxide, and cumene hydroperoxide.
 12. The method of preparing an acryl-based impact reinforcement according to claim 1 wherein b) the latex having small particles is prepared by a polymerization method comprising: i) polymerization of a first emulsified mixture comprising 97.0 to 99.9 parts by weight of alkyl acrylate having an alkyl group of C₂ to C₈; 0.1 to 3.0 parts by weight of cross-linking agent; 0.01 to 3.0 parts by weight of a polymerization initiator; 20 to 80 parts by weight of an emulsifier; and 1000 parts by weight of ion-exchange water at 60 to 80° C. to prepare a first seed comprising a first latex; ii) polymerization of a second emulsified mixture comprising 97.0 to 99.9 parts by weight of alkyl acrylate having an alkyl group of C₂ to C₈; 0.1 to 3.0 parts by weight of cross-linking agent; 0.1 to 4.0 parts by weight of an emulsifier; and 80 parts by weight of ion-exchange water, by adding 0.01 to 3.0 parts by weight of a initiator to the seed while adding the emulsified mixture continuously to the first seed, to form a second latex; iii) polymerization of a third emulsified mixture comprising 97.0 to 99.9 parts by weight of alkyl acrylate having an alkyl group of C₂ to C₈; 0.1 to 3.0 parts by weight of cross-linking agent; 0.1 to 4.0 parts by weight of an emulsifier; and 80 parts by weight of ion-exchange water, by adding 0.01 to 3.0 parts by weight of a initiator to the second latex while adding the emulsified mixture continuously to the second latex, to form a third latex; and iv) polymerization of a fourth emulsified mixture comprising 80 to 100 parts by weight of alkyl methacrylate having an alkyl group of C₁ to C₄; 10 parts by weight or less of alkyl acrylate selected from the group consisting of ethyl acrylate, methyl acrylate, and butyl acrylate; 10 parts by weight or less of nitrile selected from the group consisting of acrylonitrile, and methacrylonitrile; 0.1 to 4.0 parts by weight of an emulsifier; and 150 parts by weight of ion-exchange water, by adding 0.01 to 3.0 parts by weight of a initiator to the third latex while adding the emulsified mixture continuously to the third latex. 